The Israeli air force is preparing to deploy a new air-defense system with the biblical name of David's Sling, designed to intercept medium-range missiles, while the Iron Dome system deployed earlier battles Palestinian rockets.

A new unit has been formed to man the first David's Sling battery that will be based in central Israel sometime in 2012.

David's Sling, also known as Magic Wand, has been jointly developed by Rafael Advanced Defense Systems and U.S. defense contractor Raytheon to counter missiles and rockets with ranges of 25-185 miles.

The interceptor, known as Stunner, is a two-stage missile that can change course in mid-flight and can operate in all weather conditions.

It will form part of the multilayered missile defense system Israel is putting in place to meet the growing threat of a sustained bombardment, possibly lasting several weeks, by missiles and rockets of all calibers and ranges, including ballistic missiles.

In the worst-case scenario, but one which Israeli military planners fear is likely, the Jewish state would be hammered by Iran and Syria as well as Hezbollah in Lebanon and Hamas and other Palestinian militants in the Gaza Strip.

Iron Dome, two batteries of which are operational, constitutes the bottom tier, designed to intercept short-range missiles, rockets and mortar shells fired by the Iranian-armed Hezbollah into northern Israel and by the Palestinians in the south.

Iron Dome was also developed by Haifa-based Rafael.

The Arrow system, developed by state-owned Israel Aerospace Industries, formed the top layers of the defense shield.

Arrow-2, the variant currently deployed, is designed to knock out ballistic missiles, primarily the Shehab-3b currently deployed by Iran, and the more advanced solid-fuel Sejjil-2 Tehran is now developing.

Arrow-3, which would be able to intercept ballistic missiles in space earlier in their trajectory, is currently under development.

According to Israeli media reports, David's Sling would also be capable of intercepting long-range missiles like the Shehab at lower altitudes if they evaded the Arrow batteries.

The only system that has so far been engaged in combat is Iron Dome, which uses two radar units built by Elta Systems, an IAI subsidiary, to calculate the trajectories of incoming missiles within moments of launch.

The computer then decides whether they will hit an inhabited area or not. If they do not, the system ignores them and pursues missiles that could cause casualties.

Each Iron Dome battery has 20 Tamir interceptors and can cover an area of up to 60 square miles.

Iron Dome scored its first kills when it made its combat debut in southern Israel earlier this year

The mobile system downed at least nine 122mm Grad rockets aimed at the Negev Desert city of Beersheba and the port of Ashkelon over several days in April, the first ever destroyed in midflight by counter-missile fire anywhere in the world.

Patriot missiles built by Raytheon Corp. shot down Scud-type ballistic missiles during the 1990-91 Gulf war. But until Iron Dome came along there was no way of intercepting short-range missiles like the Grads and the mortar shells that Hamas use.

In August, the two Iron Dome batteries, one based outside Beersheba and the other outside Ashkelon, downed 18 rockets fired at the cities. But some evaded the systems, causing some casualties and damage.

The military blamed unspecified "technical problems." But the Defense Ministry has had to admit that, as many in Israel had expected, Iron Dome is not infallible, particularly if large numbers of Grads and similar rockets are launched in salvos.

A third battery is being put together to bolster defenses in the south. But the military acknowledges that it could take 15-20 Iron Dome batteries to effectively cover the northern and southern border areas anywhere near effectively.

But Hezbollah and the Palestinians in Gaza are acquiring longer range weapons that can reach Israel's narrow central region.

This makes Tel Aviv, Israel's main urban conurbation containing two-thirds of the population, its industrial heartland and many strategic installations, increasingly vulnerable.

David's Sling is thus needed to provide some defense there, but if the shooting starts multiple batteries will be needed.

One reason there are still only two Iron Dome batteries deployed is that the government was slow to acknowledge the need for such systems and does not have the funds.